Biodegradable resin compositions

ABSTRACT

The present invention provides a biodegradable resin composition with improved biodegradability or with an additional useful function (antibacterial properties), while maintaining the mechanical properties of the biodegradable resin. More specifically, the present invention provides a biodegradable resin composition containing a biodegradable resin such as a polylactic acid polymer and a mamman digestion product such as a mannooligosaccharide. The present invention further provides various biodegradable products produced by molding this biodegradable resin composition into desired shapes.

TECHNICAL FIELD

[0001] The present invention relates to biodegradable resincompositions. More specifically, the present invention relates to abiodegradable resin composition that can be produced at reduced costwhile maintaining the strength and physical properties of thebiodegradable resin; a biodegradable resin composition with improvedbiodegradability; and a resin composition having an additional usefulfunction.

BACKGROUND ART

[0002] Plastics have conventionally been used in a wide variety offields because they are lightweight, durable and excellent in moldingprocessability. On the other hand, however, plastics decompose verylittle under natural environmental conditions. Therefore, if disposed ofby underground burial, plastics remain almost permanently. If plasticsare disposed of by incineration, problems arise such as the generationof toxic gas or damage to the incinerator. The disposal of plastics hasbeen focused on as an environmental problem.

[0003] Therefore, with the purpose of protecting the global environment,there have been active attempts to develop biodegradable resins.Biodegradable resins are currently classified into the following groups:

[0004] chemically synthesized resins such as polycaprolactone,polylactic acid, polyvinyl alcohol, polybutylene succinate andcopolymers thereof;

[0005] microbially produced resins such as polyhydroxybutyrate/valeratecopolymers; and

[0006] natural product-derived resins such as acetyl cellulose.

[0007] Further, there is a proposal to add starch or processed starch tothese resins in order to reduce the cost and improve biodegradability(Japanese Unexamined Patent Publications Nos. 14228/1990, 31333/1991,248851/1992, 331315/1993 and 207047/1994).

[0008] The addition of starch, etc. to biodegradable resin improvesbiodegradability but severely reduces strength, elongation (%) and likemechanical properties required of the resin composition and moldingsthereof, thus causing the problem that the resulting products becomefragile. Therefore, in reality, there is a limitation on the proportionof starch to resin and the desired cost reduction has not yet beenachieved.

DISCLOSURE OF INVENTION

[0009] An object of the present invention is to provide a biodegradableresin composition with improved biodegradability while substantiallymaintaining the mechanical properties of the biodegradable resin.Another object of the invention is to provide a biodegradable resincomposition that can be produced at reduced cost while substantiallymaintaining the mechanical properties of the biodegradable resin. Afurther object of the invention is to provide a biodegradable resincomposition with an additional useful function while substantiallymaintaining the mechanical properties of the biodegradable resin.

[0010] The present inventors carried out intensive research day andnight to achieve the above objects and found that the addition of amannan digestion product to a biodegradable resin can provide a resincomposition with improved biodegradability and furthermore can producethe resin composition and moldings thereof at a lower cost than thesingle use of biodegradable resin while the mechanical properties of theresin composition and moldings thereof are substantially equivalent tothose of the biodegradable resin and moldings thereof. The inventorsfurther found the following specific effect of the resin compositioncomprising a biodegradable resin and a mannan digestion product: theresin composition can adsorb bacteria to different degrees depending onthe mannan digestion product content of the resin composition. Theinventors confirmed that various products with antimicrobial barrierproperties can be produced by using the above-mentioned resincomposition. The bacterial adsorption or adhesion peculiar to the resincomposition of the invention is presumably one of the causes of theexcellent biodegradability of the resin composition of the invention.The present invention has been developed based on these novel findings.More specifically, the invention provides the following biodegradableresin compositions:

[0011] Item 1. A biodegradable resin composition comprising abiodegradable resin and a mannan digestion product.

[0012] Item 2. The biodegradable resin composition according to item 1wherein the biodegradable resin is an aliphatic polyester.

[0013] Item 3. The biodegradable resin composition according to item 1wherein the biodegradable resin is at least one member selected from thegroup consisting of polyhydroxybutyrate, polylactic acid,polycaprolactone, polybutylene succinate, polybutylenesuccinate/adipate, polybutylene succinate carbonate, polyvinyl alcoholand cellulose acetate.

[0014] Item 4. The biodegradable resin composition according to item 1wherein the biodegradable resin is a polylactic acid polymer.

[0015] Item 5. The biodegradable resin composition according to item 4wherein the polylactic acid polymer is a a homopolymer or copolymer oflactic acid (polylactic acid), or at least one copolymer of lactic acidand at least one member selected from the group consisting of cycliclactone, glycolic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid,α-hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid,hydroxyheptanoic acid, hydroxyoctanoic acid, ethylene glycol,polyethylene glycol, 1,4-butanediol, succinic acid and sebacic acid.

[0016] Item 6. The biodegradable resin composition according to item 1wherein the biodegradable resin is a polylactic acid.

[0017] Item 7. The biodegradable resin composition according to item 1wherein the biodegradable resin has a number average molecular weight of20,000 or more and a melting point of 70° C. or higher.

[0018] Item 8. The biodegradable resin composition according to item 1wherein the mannan digestion product is at least one member selectedfrom the group consisting of mannooligosaccharides, galactomannandigestion products and glucomannan digestion products.

[0019] Item 9. The biodegradable resin composition according to item 1wherein the proportion of the mannan digestion product is 0.05 to 40 wt.% relative to 100 wt. % of the biodegradable resin.

[0020] Item 10. The biodegradable resin composition according to item 1wherein the proportion of the mannan digestion product is 1 to 40 wt. %relative to 100 wt. % of the biodegradable resin.

[0021] Item 11. The biodegradable resin composition according to item 1which further comprises a crystal nucleating agent.

[0022] Item 12. The biodegradable resin composition according to item 11wherein the crystal nucleating agent is at least one member selectedfrom the group consisting of talc, boron nitride, calcium carbonate,magnesium carbonate and titanium oxide.

[0023] The present invention further provides moldings produced bymolding the above biodegradable resin compositions. Such moldingsinclude, for example, biodegradable products and products withantimicrobial barrier properties.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] The mannan digestion product used in the present invention is acompound formed by the digestion of mannan and comprising mannose.

[0025] Mannans are polysaccharides mainly consisting of mannose andinclude those classified into the following classes:

[0026] (1) Plant-derived mannans: such mannans include copra meal andflakes from coconut palms, Heacra Palm (a plant of the palm familyoriginating in South Africa), tsukuneimo (a type of yam) mannan, andyamaimo (Japanese yam) mannan.

[0027] (2) Glucomannans: polysaccharides comprising glucose and mannose.Such mannans include, for example, mannans from konjac tubers, lily,narcissus and the subterranean stem of Lycoris radiata.

[0028] (3) Galactomannans: polysaccharides comprising galactose andmannose. Such mannans include, for example, mannans from locust beangum, soybean hulls derived from soybean seed coat, tamson gum, tara gum,guar gum, etc.

[0029] (4) Other mannans: mannans composed of mannose and at least twoother sugars. Such mannans include D-galacto-D-gluco-D-mannan containedin the wood of conifers, and mannan from xanthan gum, etc.

[0030] The mannan digestion product used in the present invention can beobtained by digesting various mannans, including those exemplifiedabove, using a suitable method. For example, the following mannandigestion methods are known: biochemical digestion methods directlyusing polysaccharide-digesting enzymes (mannanase, galacto-mannanase,gluco-mannanase, etc.) or bacteria producing such enzymes; chemicaldigestion methods using acids or alkalis; and physical digestion methodsusing high speed stirrers or shearers. A wide variety of mannandigestion products obtained by the above digestion methods can be usedin the present invention. The mannan digestion product used in thepresent invention may be obtained by any of the above digestion methods.However, the mannan digestion product production method is not limitedthereto.

[0031] The mannan digestion product includes, for example, β-1,4mannobiose, β-1,4 mannotriose, β-1,4 mannotetraose, methyl β-mannosideand like β-1,4 mannooligosaccharides; β-1,6 galactomannooligosaccharide,β-1,4 galactomannooligosaccharide, α-1,6 galactomannooligosaccharide,α-1,3 galactomannooligosaccharide and like mannooligosaccharides inwhich one or two galactoses are bonded to β-1,4 mannobiose, β-1,4mannotriose or β-1,4 mannotetraose to form branched structure;galactomannan digestion products such as oligosaccharides obtained bydigestion of copra lees, coffee lees, guar gum or locust bean gum withmannanase; oligosaccharides wherein glucose or maltose is bonded via aβ-1,4 bond to mannotriose, mannotetraose or the like; and glucomannandigestion products contained in konjac.

[0032] For the sake of convenience, commercially available mannandigestion products may be used in the present invention. Alternatively,for example, galactomannan digestion products can be obtained byextracting galactomannan from the seeds of locust, tara or guar plantsby water extraction or alcohol precipitation and then digesting thegalactomannan with an acid or an enzyme such as galactomannanase andisolating the fraction with a molecular weight of 5,000 to 50,000,preferably 10,000 to 20,000. It is also possible to produce glucomannandigestion products by swelling konjac powder with water to produce akonjac paste and digesting the konjac paste with glucomannanase. Thesemannan digestion products may be purified or roughly purified productsand can be formed into any desired shapes, for examples, aqueoussolutions, gels and like liquids, semi-liquids, powders, granules andlike solids, or dried products.

[0033] It is also possible to use mannan digestion product derivativesas mannan digestion products in the invention. Mannan digestion productderivative means a wide variety of compounds produced by a dehydrationcondensation reaction for forming a chemical bond between the hemiacetalhydroxyl group of a mannan digestion product and other substance. Theother substance bound to the hemiacetal hydroxyl group includes, forexample, ribose, ascorbic acid, acrylic acid, styrene, higher alcoholsand derivatives thereof, and aliphatic ethers, long-chain epoxyderivatives and the like. Examples of useful mannan digestion productderivatives include isopropylidene derivatives, benzylidene derivatives,butylene glycol derivatives, polyalcohol derivatives and pyrrolidonederivatives.

[0034] The biodegradable resin used in the present invention means aresin (plastic) digested by the action of microorganisms or enzymesexisting in nature such as the soil or sea. Any known biodegradableresin may be used as the biodegradable resin. Useful resins include, forexample, microbially produced resins, natural high molecular weightresins, synthesized high molecular weight resins and natural-syntheticpolymer composite resins. Specific examples include aliphatic polyesterssuch as polycaprolactone, polylactic acid, polyhydroxybutyrate/valerate;polyvinyl alcohols, acetyl cellulose, methyl cellulose, ethyl cellulose,poly-β-hydroxybutyric acid and copolymers thereof; polybutylenesuccinate and copolymers thereof; and a starch-caprolactone complex.

[0035] Aliphatic polyesters and polyvinyl alcohols are preferred.Especially preferred are aliphatic polyesters, which are comparativelylow-cost thermoplastic resins with excellent heat resistance and can bemelted and molded.

[0036] Prototype and commercially available biodegradable plasticscomposed of polyvinyl alcohols include, for example, “Poval” (tradename, product of Kuraray Co., Ltd.).

[0037] Examples of aliphatic polyesters include polyester resins such asa resin comprising 3-hydroxybutyric acid homopolymer or a copolymer of3-hydroxybutyric acid and other hydroxy fatty acid; polylactic acidresins, polycaprolacton resins, and aliphatic polyesters mainlyconsisting of glycol and an aliphatic dicarboxylic acid or an anhydridethereof. Prototype and commercially available aliphatic polyester resinsinclude, for example, the resins known by the trade name “Biopol”(polyhydroxybutyrate/hydroxyvalerate copolymer, product of MonsantoJapan, Ltd.), the trade name “Lacea” (polylactic acid, product of MitsuiChemicals, Inc.), the trade name “Lacty” (polylactic acid, product ofShimadzu Corporation), the trade name “EcoPLA” (polylactic acid, productof Cargill Dow Polymers, LLC), the trade name “Iupec” (polybutylenesuccinate carbonate, product of Mitsubishi Gas Chemical Company, Inc.),the trade name “Lunare SE” (polyethylene succinate, product of NipponShokubai Co., Ltd.), the trade name “Bionolle #1000” (polybutylenesuccinate, product of Showa Highpolymer Co., Ltd.), the trade name“Bionolle #3000” (polybutylene succinate/adipate copolymer, product ofShowa Highpolymer Co., Ltd.), and the trade names “Celgreen PH” and“Celgreen P-HB” (polycaprolactones, products of Daicel ChemicalIndustries, Ltd.).

[0038] Also usable are blends prepared by mixing these aliphaticpolyesters and starch. Commercially available blend products include,for example, “Mater-Bi” manufactured by The Nippon Synthetic ChemicalIndustry Co., Ltd. and “Novon” manufactured by Chisso Corporation. Theresins mentioned above may be used in mixtures of two or more.

[0039] Of these aliphatic polyesters, especially preferred are aliphaticpolyesters consisting chiefly of glycol and an aliphatic dicarboxylicacid or an anhydride thereof, and polylactic acid polymers.

[0040] Examples of useful glycols include ethylene glycol,1,4-butanediol, 1,8-hexanediol, decamethylene glycol, neopentylglycoland 1,4-cyclohexane dimethanol. These glycols may be used incombinations of two or more. Examples of aliphatic carboxylic acids (oranhydrides thereof) include succinic acid, adipic acid, suberic acid,sebacic acid, dodecanoic acid, succinic anhydride and anhydrous adipicacid. These acids may be used in combinations of two or more. Usefulaliphatic polyesters further include high molecular weight aliphaticpolyesters produced by a coupling reaction using diisocyanate,oxazoline, diepoxy compounds or other coupling agents.

[0041] Examples of polylactic acid polymers include homopolymers orcopolymers comprising lactic acid as a monomer component (polylacticacids), copolymers of lactic acid and one or more kinds of compoundsselected from: cyclic lactones such as ε-caprolactone; oxyacids such asglycolic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid,α-hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid,hydroxyheptanoic acid and hydroxyoctanoic acid; glycols such as ethyleneglycol, polyethylene glycol and 1,4-butanediol; dicarboxylic acids suchas succinic acid and sebacic acid. Random copolymers and/or blockcopolymers may be used as the copolymer. Preferred are polylactic acids.

[0042] Useful polylactic acids include lactic acid homopolymers. Alsousable are copolymers prepared by copolymerization of lactic acid with apolyethylene glycol having a molecular weight of 600 or more in a molarproportion of 0.1 to 10%, an aliphatic polyester in a molar proportionof 0.1 to 80% or polycaprolactone in a molar proportion of 0.1 to 80%.Preferable are copolymers prepared by copolymerization of lactic acidwith a polyethylene glycol having a molecular weight of 2,000 to 20,000in a molar proportion of 0.1 to 10%, an aliphatic polyester in a molarproportion of 0.1 to 50% or polycaprolactone in a molar proportion of0.1 to 50%.

[0043] Lactic acid is a stereoisomeric monomer and exists as L-lacticacid and D-lactic acid. Either isomer or a mixture of these isomers maybe used as lactic acid in the invention. It is preferable to have anoptical purity of at least 60%, more preferably 80% or higher. When theoptical purity is low, the polymer tends to have low crystallinity,resulting in low heat resistance and inferior mechanical properties.When high elasticity is desired, the proper proportion of L-lactic acidis 70% or more, preferably 90% or more.

[0044] The biodegradable resins used in the present invention may beprepared by conventional methods. For example, polylactic acids can beprepared by known methods such as direct dehydration andpolycondensation of lactic acid; or a method comprising dehydration oflactic acid into lactide and then subjecting the lactide to ring openingpolymerization. It is convenient to use commercially availablebiodegradable resins. Examples of prototype and currently commerciallyavailable biodegradable plastics include, in addition to the alreadymentioned plastics, those known by the trade name “Biogreen”(polyhydroxybutyrate, product of Mitsubishi Gas Chemical Company, Inc.),the trade name “Cornpol” (modified starch, product of Japan Corn StarchCo., Ltd.), the trade name “Celgreen PCA” (cellulose acetate, product ofDaicel Chemical Industries, Ltd.), the trade name “Dolon CC”(chitosan/cellulose/starch, product of Aicello Chemical Co., Ltd.), andthe trade name “Celgreen” (cellulose acetate-based material, product ofDaicel Chemical Industries, Ltd.).

[0045] From the viewpoint of mechanical strength, it is preferable forthe biodegradable resin of the invention to have a number averagemolecular weight of about 20,000 or more, preferably 40,000 or more,more preferably 60,000 or more, even more preferably 100,000 or more.From the viewpoint of heat resistance, it is preferable that thebiodegradable resin have a melting point of 70° C. or higher, morepreferably 100° C. or higher, even more preferably about 160° C.

[0046] The proportions of the biodegradable resin and the mannandigestion product vary depending on the kinds of resin and product.Therefore, it is difficult to specifically define the proportions.Generally, the degradation rate and functions of the biodegradable resincomposition such as bacterial adsorption can be adjusted by changing theproportion of mannan digestion product to biodegradable resin. Thebiodegradability and bacterial adsorption properties can be enhanced byincreasing the proportion of mannan digestion product. The resultingcomposition can suitably be used for objects requiring antimicrobialbarrier properties and rapid degradability. When high strength isrequired, it is desirable to use galactomanno-oligosaccharide containing80% or less of mannose as a mannan digestion product. The preferableproportional ranges of the components greatly differ depending on theintended use of the resin composition. The proportions can suitably bedecided in view of the balance between physical properties such asstrength and functions such as bacterial adsorption andbiodegradability.

[0047] From the viewpoint of mechanical strength, it is adequate thatthe proportion of the mannan digestion product be usually 0.05 to 40 wt.%, preferably 0.5 to 10 wt. %, more preferably 1 to 5 wt. %, relative to100 wt. % of the biodegradable resin.

[0048] From the viewpoints of degradation rate (biodegradability) andbacterial adsorption, it is adequate that the proportion of the mannandigestion product be usually 1 to 40 wt. %, preferably 5 to 20 wt. %,more preferably 5 to 10 wt. %, relative to 100 wt. % of thebiodegradable resin.

[0049] With the purpose of functional improvement or addition of a newfunction, additives may be incorporated into the biodegradable resincomposition in any proportions. Such additives include, for example,pigments, antioxidants, antistatic agents, matting agents, antiagingagents, fluorescent brighteners, UV absorbents, UV stabilizers,lubricants, fillers, carbon black, thickeners, chain extenders,crosslinking agents, crystal nucleating agents, plasticizers,stabilizers and viscosity stabilizers. The addition of a crystalnucleating agent such as talc, boron nitride, calcium carbonate,magnesium carbonate or titanium oxide is especially preferred because itpromotes crystallization during the thermoforming process and improvesthe heat resistance and mechanical strength of the molding. As long asthe effects of the invention are not adversely affected, starch andprocessed starch, pectin, chitin, chitosan, alginic acid or a saltthereof, xylose, cellulose or a cellulose derivative such ascarboxymethylcellulose may also be added.

[0050] The biodegradable resin composition of the invention can beprepared by mixing the above biodegradable resin and the mannandigestion product with heating.

[0051] The method for mixing the biodegradable resin and the mannandigestion product is not specifically limited. Useful methods include amethod comprising adding a mannan digestion product to a biodegradableresin while heating the resin, and mixing using a kneader such as a rollmill; a method comprising melting and kneading a mannan digestionproduct and a biodegradable resin in an extruder; blow molding; and foammolding. The heating temperature is usually in the range of 120° C. to250° C. From the viewpoint of biodegradability, the range of 120° C. to160° C. is preferable.

[0052] The biodegradable resin composition obtained can be processed,for example, by a method comprising heating and injecting thecomposition into an extrusion mold or can be dissolved in a solvent andformed into membranes, sheets, films or nets.

[0053] The biodegradable resin composition of the invention can thus beformed into various shapes such as films, sheets, plates, foams andbottles. Therefore, the composition can suitably be used for thefollowing variety of purposes: packaging materials such as trays, foamtrays, stretch films, shrink films, beverage bottles, and blisterpackaging for toothbrushes; agricultural and gardening materials such asgreenhouse films, tunnel films, multi-purpose films, vegetation films,seedling pots, seed strings, and covering materials for fertilizers andpesticides; civil engineering materials such as vegetation nets, heavybags, construction molds, civil engineering sheets and grass stakes;fishery materials such as fishing nets, laver nets, cultivation nets,fishing lines and fishing bait bags; waterproof sheets and packagingmaterials such as paper diapers and sanitary products; medicalappliances such as syringes; commodities and sundry articles such asgarbage bags, shopping bags, plastic bags, drain nets, laminatedcontainers for dishes, spoons and forks, binding tapes, toothbrush andrazor handles, shampoo and conditioner bottles, cosmetic bottles, pensand markers; medical materials such as osteosynthesis materials, suturematerials and wound covering materials; air cleaning filters; magneticcards, labels, mold release papers, golf tees, etc.

[0054] The biodegradable resin composition of the invention, as it is orafter being formed into the desired shape, can be used as a blend byadding the composition to a suitable biodegradable resin. This use canreduce the costs of conventional biodegradable resins and biodegradableresin products (moldings) prepared using such resins and also improvebiodegradability. Furthermore, new functions (antimicrobial barrierproperties) can be imparted to conventional biodegradable resins.

EXAMPLES

[0055] Examples are given below to illustrate the invention in moredetail, but it is to be understood that the invention is not limitedthereby.

Example 1

[0056] Galactomannooligosaccharide (product of C.P.R Co., Ltd.) was usedas a mannan digestion product. Polylactic acid (“Lacty #9000”manufactured by Shimadzu Corporation) was used as a biodegradable resin.The polylactic acid, talc and galactomanno-oligosaccharide were mixed ata weight ratio of 50:40:10 and kneaded in a Brabender Plastograph at120° C. for 30 minutes. Polylactic acid (“Lacty #1012” manufactured byShimadzu Corporation) was further added to the mixture at a weight ratioof 1:1 and kneaded in a high-speed mixer for 30 minutes. The resultingmixture was melted by heating and formed into pellets using a testextruder. The pellets were molded into a sheet with a thickness of about500 μm [“Lacty #1012”: (“Lacty #9000” 50%/talc40%/galactomanno-oligosaccharide 10%) =50:50]. This sheet was cut to asize of 100 mm×100 mm and tested.

Comparative Example 1

[0057] A resin composition was prepared in the same manner as in Example1 except that talc was used in place of galactomannooligosaccharide, andmolded into a sheet [“Lacty #1012”: (“Lacty #9000” 50%/talc 50%)=50:50].

Comparative Example 2

[0058] A resin composition was prepared in the same manner as in Example1 except that corn starch was used in place of talc andgalactomanno-oligosaccharide, and molded into a sheet [“Lacty #1012”:(“Lacty #9000” 50%/corn starch 50%) =50:50].

Experiment Examples

[0059] The sheets of the biodegradable resin compositions prepared inExample 1 and Comparative Examples 1 and 2 were measured with respect tothe following parameters to evaluate their physical properties andfunctionalities:

[0060] 1. Mechanical Properties

[0061] Fracture strength and fracture elongation were measured inaccordance with JIS K-7113 at 17° C. at a humidity of 50%. Table 1 showsthe results. Fracture strength and fracture elongation were calculatedfrom the following formulas:

Fracture strength (N/cm²)=Fracture load (N)/Cross section (cm²)

Fracture elongation (%)=[(Fracture elongation−Span length)/Spanlength]×100

[0062] TABLE 1 Example 1* Comp. Ex. 1* Comp. Ex. 2 Thickness (mm) 0.5030.491 0.504 Fracture strength 4448.9 4753.5 3364.0 (N/cm²) Fractureelongation (%) 1.4 1.8 1.5

[0063] These results confirm that the addition of a mannan digestionproduct to a biodegradable resin hardly affects the mechanicalproperties of the biodegradable resin such as fracture strength andfracture elongation.

[0064] 2. Evaluation of Biodegradability

[0065] Flat plate films (10 cm×10 cm×0.2 cm thick) were prepared inaccordance with the processes described in Example 1 and ComparativeExample 1. Five sheets each of these films were buried 1) in activatedsludge and 2) in soil. The biodegradability was evaluated from changesin weight. Reduction in weight (weight loss %) indicates the degree ofbiodegradation of the flat plate film. Table 2 shows the results. InTable 2, Example 1 represents the average of 9 samples, and ComparativeExample 1 represents the average of 5 samples. TABLE 2 Weight loss %Example 1 Comparative Example 1 1) Biodegradability in activated sludge(sewage treatment plant) Start (0 hour) 0 0 1 month later 86.1 30.1 2months later 91.6 63.2 3 months later 98.1 78.5 2) Biodegradability insoil Start (0 hour) 0 0 1 month later 68.6 16.4 2 months later 88.4 40.93 months later 92.1 54.3

[0066] These results confirm that the addition of a mannan digestionproduct to a biodegradable resin significantly improves thebiodegradability of the resin.

[0067] 3. Evaluation of Bacterial Adsorption Capability

[0068] Flat plate films (10 cm×10 cm×0.2 cm thick) were prepared inaccordance with the processes described in Example 1 and ComparativeExample 1. Five sheets each of these films were placed into 500 mlflasks containing 100 ml of a bacteria culture medium (Escherichia coli,bacteria count: 2×10⁸ bacteria/ml) and shaken. Then, the films weretaken out and the bacterial count in the medium was determined. Theadsorption % was determined from the reduction in bacterial count. Table3 shows the results. In Table 3, Example 1 represents the average of 9samples, and Comparative Example 1 represents the average of 5 samples.TABLE 3 Bacterial adsorption % Example 1 Comparative Example 1 Start (0hour) 0 0 10 minutes later 27.8 0.2 30 minutes later 84.5 0.9 60 minuteslater 90.9 4.3

[0069] The results confirm that the biodegradable resin composition ofthe invention containing a mannan digestion product in addition to abiodegradable resin has greatly improved bacterial adsorptioncapability.

INDUSTRIAL APPLICABILITY

[0070] The biodegradable resin composition and moldings thereofaccording to the present invention rapidly decompose completely innature such as in soil or in water by the action of enzymes or bacteriawithout generating toxic substances. Therefore, after use, thebiodegradable resin composition and moldings thereof can be disposed of,as they are or after grinding, by underground burial or underwaterdisposal.

[0071] Especially, the biodegradable resin composition of the inventionprepared using a polylactic acid polymer as a biodegradable resin istransparent and useful as a biodegradable plastic (biodegradableproduct) with excellent toughness, flexibility and impact resistance.Therefore, this resin composition can suitably be used for variouspurposes especially requiring strength, such as beverage bottles,shampoo and conditioner bottles, cosmetic bottles and like polyethyleneterephthalate (PET) bottles; civil engineering materials such asconstruction molds and piles; fishery materials such as fishing nets andfishing lines; agricultural materials for vegetation and plasticgreenhouses; vegetation materials; laminated containers for spoons andforks; toothbrush and razor handles; medical materials such asosteosynthesis materials and suture materials; sports goods such as golftees; writing supplies such as pencil cases and plastic sheets laidunder writing paper; clothing and industrial textile products;sanitation and medical related materials such as diapers, sanitaryproducts, gauzes and patches.

[0072] By adjusting the proportion of the mannan digestion product, thebiodegradable resin composition of the invention is further providedwith bacterial adsorption capability. For example, if using textileproducts (clothing) made from such a biodegradable resin composition,bacteria once adsorbed on the products are difficult to desorb, wherebythe dispersion of bacteria can be prevented. Such products are useful,for example, as antimicrobial barrier textile products effective for theprevention of nosocomial infection.

[0073] By adding a mannan digestion product to a biodegradable resin,the present invention can provide a biodegradable plastic (abiodegradable product) at a lower cost than single use of thebiodegradable resin, while substantially maintaining the mechanicalproperties at the level achieved by a biodegradable plastic (abiodegradable product) composed of the biodegradable resin alone.

1. A biodegradable resin composition comprising a biodegradable resin(except for fine cellulose) and a mannan digestion product.
 2. Thebiodegradable resin composition according to claim 1 wherein thebiodegradable resin is an aliphatic polyester.
 3. The biodegradableresin composition according to claim 1 wherein the biodegradable resinis at least one member selected from the group consisting ofpolyhydroxybutyrate, polylactic acid, polycaprolactone, polybutylenesuccinate, polybutylene succinate/adipate, polybutylene succinatecarbonate, polyvinyl alcohol and cellulose acetate.
 4. The biodegradableresin composition according to claim 1 wherein the biodegradable resinis a polylactic acid polymer.
 5. The biodegradable resin compositionaccording to claim 4 wherein the polylactic acid polymer is ahomopolymer or copolymer of lactic acid (polylactic acid), or at leastone copolymer of lactic acid and at least one member selected from thegroup consisting of cyclic lactone, glycolic acid, α-hydroxybutyricacid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, hydroxypentanoicacid, hydroxycaproic acid, hydroxyheptanoic acid, hydroxyoctanoic acid,ethylene glycol, polyethylene glycol, 1,4-butanediol, succinic acid andsebacic acid.
 6. The biodegradable resin composition according to claim1 wherein the biodegradable resin is a polylactic acid.
 7. Thebiodegradable resin composition according to claim 1 wherein thebiodegradable resin has a number average molecular weight of 20,000 ormore and a melting point of 70° C. or higher.
 8. The biodegradable resincomposition according to claim 1 wherein the mannan digestion product isat least one member selected from the group consisting ofmannooligosaccharides, galactomannan digestion products and glucomannandigestion products.
 9. The biodegradable resin composition according toclaim 1 wherein the proportion of the mannan digestion product is 0.05to 40 wt. % relative to 100 wt. % of the biodegradable resin.
 10. Thebiodegradable resin composition according to claim 1 wherein theproportion of the mannan digestion product is 1 to 40 wt. % relative to100 wt. % of the biodegradable resin.
 11. The biodegradable resincomposition according to claim 1 which further comprises a crystalnucleating agent.
 12. The biodegradable resin composition according toclaim 11 wherein the crystal nucleating agent is at least one memberselected from the group consisting of talc, boron nitride, calciumcarbonate, magnesium carbonate and titanium oxide.
 13. A biodegradableproduct produced by molding the biodegradable resin composition ofclaim
 1. 14. A product with antimicrobial barrier properties producedfrom the biodegradable resin composition of claim 1.